Cassandra Mortmain is 17. Her journal describes the weird and wonderful world in which she lives: housed in a crumbling castle, with her writer father (who is "blocked"), her beautiful older sister Rose, her brainy younger brother and her unconventional artist stepmother, Topaz. The sudden arrival of two handsome American strangers is the catalyst for this touching coming-of-age tale, which sees Cassandra taking her first forays in womanhood not without her fair share of grief and giggles.